/Engine/Source/Runtime/UMG/Public/Blueprint/WidgetTree.h
Iterates through all widgets including widgets contained in named slots, other than investigating named slots. This includes foreign widget trees inside of other UserWidgets.
void ForEachWidgetAndDescendants ( [TFunctionRef](API\Runtime\Core\GenericPlatform\TFunctionRef)< void([UWidget](API\Runtime\UMG\Components\UWidget) *)> Predicate ) const